1. Field of the Invention
This invention relates to improvements in imaging methods, apparatuses, and circuits, and more particularly to such improvements using x-ray or light radiation for uses such as in medical or document imaging procedures, or the like.
2. Technical Background
Heart disease is one of the most prevalent and lethal diseases, especially for older people throughout the world. Prospective medical screening of large numbers of people is not now possible.
Recently, efforts have been directed to improving x-ray images, particularly in soft tissue detection environments such as coronary arteriography for prospective screening of coronary occlusive heart disease.
Digital subtraction angiography (DSA) is a medical procedure of increasing importance in the diagnosis and treatment of heart disease. The technique is used to form x-ray images of the arteries and blood vessels of the heart to look for constriction. One problem is that a normal x-ray image does not distinguish blood from other tissue. The DSA technique achieves the separation by adding iodine (or other contrast medium) to the blood, and looking at the difference in x-ray images taken at energies above and below the iodine x-ray absorption edge (the K-edge). This allows selective imaging of the blood, because it is the only part of the body containing the iodine.
One method that is becoming increasingly popular uses synchrotron radiation as the source of the two x-ray beams at the different wavelengths. The slit-shaped beams above and below the K-edge intersect the patient's heart and are detected by a pair of linear sensor arrays on the other side. The patient is then moved across the beam to form a two-dimensional image. This technique is called K-edge subtraction angiography. One of the main difficulties with this technique is that the sensors and electronics must have a large dynamic range and very good linearity.
Proposals, such as that of Fukagawa et al., Review of Scientific Instruments, 60 (7) July, 1989, pages 2268-2271, advance schemes that disperse an x-ray beam of single wavelength, and acquire an image of that wavelength at one time. Then, the beam disbursal spectrometer is changed, and an image at another wavelength is acquired. The disbursal of the beam causes low average intensity and a longer exposure time. Also, the time between the first and second exposures, and the time of the two exposures, cause a blurring of the moving arteries.
Hasegawa et al., Review of Scientific Instruments, 60 (7) July, 1989, pages 2284-2286 show an imaging system composed of a linear array of amorphous silicon. The array is mechanically scanned across the x-ray beam area to form an image line-by-line. This technique is limited by the mechanical scanning time. The scanning fixture also takes up appreciable space and will grow as scanning speed is increased.
Anno et al., "Animal Experiments By K-edge Subtraction Angiography By Using SR (abstract)", Review of Scientific Instruments, 60(7), July, 1989, page 2230, describe animal experiments using a synchrotron radiation DSA unit and the images obtained are subtracted. Anno et al. noted that real time A/D converter and frame buffering memories have not been available, until now.
Nishimura et al., "High-Speed Image-Acquisition System For Energy Subtraction Angiography", Review of Scientific Instruments, 60(7), July, 1989, page 2290, disclose a method of rapid and successive acquisition of two dimensional images in a digital processing system that uses a pair of video cameras, a shutter operation, and a beam splitting apparatus, in iodine K-edge subtraction angiography using synchrotron radiation. Through the logarithmic subtraction of the two images, the signals arising from soft tissue and bone are suppressed, enhancing the signals from the iodine contrast medium. The technique employs the two video cameras to capture images within a few milliseconds of the other. The Hoyt incident x-ray is reflected by an asymmetrically cut silicon single crystal. The optical output of the radiation source above the K-edge is received by the first camera, with the second camera closed to light reception. Subsequently, the shutters of the cameras are reversed and the second camera receives the light resulting from the x-rays below the K-edge. In this case, the light to the first camera is closed. The images from the two cameras are then subtracted one from the other. The method by which the images are subtracted is not disclosed.
Fukagawa et al., "Real Time K-edge Subtraction X-ray Imaging", Review of Scientific Instruments, 60(7), July, 1989, page 2268, disclose an x-ray K-edge subtraction television system for non-invasive angiography using synchrotron radiation. The image to be detected, including a contrast material, is irradiated by monochromitized dual energy x-ray flux, or alternately, by a high speed monochromator, so that the object is irradiated by the flux above and below the K-edge photon energy of the contrast material. The television cameras receive the respective images above and below the K-edge photon energy, to produce video signals that are processed to display the subtraction images of pairs of successive images in real time. In the system, the photon energy of x-rays is changed synchronously with the television frames. The video signal of each frame is memorized and the difference images of the video signals of pairs of successive images are shown. In the one color camera method, the higher energy x-ray images are picked up as red images and the lower energy ones as blue images with electronic shutters combined with color filters. The images are stored and read out by an analog subtraction circuit to be displayed on a black and white monitor to display the energy subtraction image. In a two camera method, two images are televised with electronic shutters timed so that the exposures for camera A and camera B correspond to the two kinds of x-ray irradiation. Each video signal (one field) is memorized in a memory A and B as image data of higher photon energy and lower one respectively. The image data are read out at the same time and fed to a digital calculation circuit to obtain an image difference signal.
Ueda et al., "A Cine K-edge Subtraction Angiographic System For Animal Studies", Review of Scientific Instruments, 60(7), July, 1989, page 2272, show a K-edge subtraction imaging system that utilizes synchrotron radiation and uses a monochromator, an x-ray television camera with a high speed shutter, and a data acquisition and control unit. Dual energy images are acquired through repetitive sequences to give a series of K-edge subtraction images. The images are subtracted by storing a digitized image in a frame memory, and subtracting the second image from the first using data processing techniques.
Audet, "High-Purity Silicon Radiation-Sensor Array For Imaging Synchrotron Radiation In Digital-Subtraction Angiography Procedures", Review of Scientific Instruments, 60(7), July, 1989, page 2276, discloses the use of a high-purity silicon radiation sensor array in digital subtraction angiography procedures using synchrotron radiation. The detector that is disclosed is a high-purity silicon radiation sensor array using a number of XY readout addresses within a DSA experimental instrumentation system.
Graeff et al., "NIKOS II-System For Non-Invasive Coronary Angiography With Synchrotron Radiation (abstract), Review of Scientific Instruments, 60(7), July, 1989, page 2328, discuss the subtraction of images with photon energies above and below the Kedge for the suppression of background contrast for amplification of contrast media structure contrast. Disclosed is a system using a beam line bending magnet.
Takeda et al., "SR High Speed K-edge Subtraction Angiography In The Small Animal (abstract)", Review of Scientific Instruments, 60(7), July, 1989, page 2320, disclose a K-edge energy subtraction system for animal experiments. The subtraction system consisted of moveable silicon &lt;111&gt; monocrystals and a digital memory system. Photon energy above and below the K-edge sequentially obtained were subtracted to produce very sharp arterial images.
In a different, but related field, current multiple color document scanning systems of high performance use line scan imaging devices to successively image one line of a document in multiple colors. There are multiple color lamps, and the line imager mechanically sits and waits as an exposure and the readout are made with each of the color lamps. The line imager then mechanically scans to the next line in the document. This is basically the same problem as at x-ray wavelengths. It is desirable to make scans of an image, in several colors, as rapidly as possible.